Very bad doctor attached to feudal arrangement (8)
I believe the answer is:
dreadful
'very bad' is the definition.
(I've seen this before)
'doctor attached to feudal arrangement' is the wordplay.
'doctor' becomes 'dr' (abbreviation).
'attached to' says to put letters next to each other.
'arrangement' is an anagram indicator.
'feudal' is an anagram of 'eadful'.
'dr'+'eadful'='DREADFUL'
(Other definitions for dreadful that I've seen before include "Terrible" , "Appalling, awful" , "Atrocious, awful" , "Dire, alarming" , "Informally very bad, perhaps the weather" .)